Work machines such as, for example, dozers, loaders, excavators, motor graders, and other types of heavy machinery use multiple hydraulic actuators to accomplish a variety of tasks. These actuators are fluidly connected to a pump on the work machine that provides pressurized fluid to chambers within the various actuators in response to operator demand. During simultaneous manipulation of the multiple actuators, it may be possible for the operator to demand fluid flow at a greater rate than the flow capacity of the pump. When a flow of fluid supplied to one of the actuators is less than demanded, that particular actuator may not respond as expected, possibly resulting in inefficient operation and/or undesired movements of the work machine.
One method of accommodating a demand for fluid flow that is greater than the capacity of an associated pump is described in U.S. Pat. No. 6,498,973 (the '973 patent) issued to Dix et al. on Dec. 24, 2002. The '973 patent describes a valve control system for a work vehicle. The valve control system includes a plurality of actuators fluidly connected to a pump. One or more of the actuators within the valve control system may be classified as a priority flow rate actuator, while the remaining actuators within the valve control system may be classified as scaled flow rate actuators. When a situation arises where a total flow rate demanded by a work machine operator for all of the actuators exceeds the pump's total flow capacity, the valve control system proportionately scales the flow supplied to the scaled flow rate actuators such that the scaled down total demanded flow rate remains within the total flow capacity of the pump. Specifically, the demanded flow rate of the priority flow rate actuators is subtracted from the maximum flow capacity of the pump to determine a flow rate available for the scaled flow rate actuators. This calculated flow rate available for the scaled flow rate actuators is then proportionately divided amongst the scaled flow rate actuators.
Although the valve control system of the '973 patent may accommodate situations where the combined flow rate demanded from priority and scaled flow rate actuators exceeds the flow capacity of the pump, the valve control system does not accommodate situations where the flow rate demanded from just the priority flow rate actuators exceeds the pumps total flow capacity. In addition, the valve control system of the '973 patent does not accommodate situations where all of the actuators are priority flow rate actuators or when importance is placed on which of the scaled flow rate actuators receive a greater portion of the remaining flow rate.
The disclosed hydraulic system is directed to overcoming one or more of the problems set forth above.